Identifying the interaction between skin temperature, maintained thermal comfort, and conduit artery shear rate through limb passive heating

Figures

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  FIGURE 1. Schematic representation of the experimental protocol. The initial 20‐min period represents the resting phase prior to baseline measurements, followed by four consecutive 10‐min steady‐state heating phases at different local temperatures (35°C arm, 35°C leg, 40°C arm, and 40°C leg). After the resting phase (baseline) and each heating phase, measurements were performed as represented in the boxes below the timeline, including blood pressure, thermal comfort (whole‐body and local), and vascular parameters (TAMV and diameter for brachial artery and superficial femoral artery, intervention and control). Time durations indicate steady‐state conditions for each thermal state. Break varied because skin temperature was allowed to return to baseline before initiating the next heating period.

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  FIGURE 2. Comparison of control arm (dashed bars) and the heated arm at three different skin temperature levels: 30°C (orange), 35°C (blue), and 40°C (white). The illustrated variables include skin temperature (a), skin blood flow (b), brachial artery shear rate (c), antegrade shear rate (d), and retrograde shear rate (e). p Values above the graphs indicate comparisons between the control and intervention arm, while p‐values above the heated arm graphs denote comparisons of measurements in the heated arm at 30°C versus 35°C and 30°C versus 40°C.

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  FIGURE 3. Comparison of control leg (dashed bars) and the heated leg at three different skin temperature levels: 30°C (orange), 35°C (blue), and 40°C (white). The illustrated variables include skin temperature (a), skin blood flow (b), superficial femoral artery shear rate (c), antegrade shear rate (d), and retrograde shear rate (e). p Values above the graphs indicate comparisons between the control and intervention leg, while p values above the heated leg graphs denote comparisons of measurements in the heated leg at 30°C versus 35°C and 30°C versus 40°C.

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  FIGURE 4. The orange line presents the mean local thermal comfort for both the arm and leg, demonstrating a strong linear correlation with skin temperature. The blue line depicts retrograde and antegrade shear rate for the brachial and superficial femoral arteries. While thermal comfort shows a linear relationship with skin temperature, the relationship between skin temperature and shear rate is generally non‐linear, with the possible exception of retrograde shear rate in the brachial artery. The balance for prolonged local limb passive heating occurs at a local thermal comfort level of 8 (“warm but fairly comfortable”), corresponding to a skin temperature of 40.32°C ± 0.31°C for the arm and 35.73°C ± 0.46°C for the leg. Shear rate values are reported at these respective temperatures (i.e., the conditions corresponding to a thermal comfort level of 8). In the brachial artery (40°C condition), retrograde shear rate is −1.05 ± 1.73 s−1 (a), while antegrade shear rate is 143.46 ± 51.48 s−1 (c). In the superficial femoral artery (35°C condition), retrograde shear rate is −12.55 ± 4.94 s−1 (b), and antegrade shear rate is 79.5 ± 14.61 s−1 (d).